**Core Concept**
Significant bacteriuria refers to the presence of a certain number of bacteria in a urine sample that indicates a urinary tract infection (UTI). The American Urological Association (AUA) and the Centers for Disease Control and Prevention (CDC) have established guidelines for defining significant bacteriuria in patients with and without symptoms.

**Why the Correct Answer is Right**
In patients with symptoms of a UTI, such as dysuria, frequency, and urgency, significant bacteriuria is defined as the presence of ≥ 10^5 (100,000) CFU (colony-forming units) of bacteria per ml of urine. This threshold is based on the idea that a higher number of bacteria is likely to indicate an infection rather than contamination. In patients without symptoms, the threshold is ≥ 10^4 (10,000) CFU per ml of urine, as the presence of a smaller number of bacteria may not be clinically significant.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the lower threshold of ≥ 10^4 (10,000) CFU per ml of urine is used for asymptomatic patients, not symptomatic patients.
**Option B:** This option is incorrect because the threshold of ≥ 10^6 (1,000,000) CFU per ml of urine is too high and not supported by current guidelines.
**Option C:** This option is incorrect because the threshold of ≥ 10^3 (1,000) CFU per ml of urine is too low and may indicate contamination rather than infection.

**Clinical Pearl / High-Yield Fact**
Remember that the diagnosis of UTI is based on the combination of clinical symptoms and the presence of significant bacteriuria, rather than just the number of bacteria in the urine.

**Correct Answer: C. ≥ 10^5 (100,000) CFU per ml of urine in symptomatic patients**